Process for manufacturing cylindrical tubular metal bodies

ABSTRACT

Metal is cast to form a bloom that is polygonal in cross section with an axial passage extending through it. Pressure is applied to one end of the hot bloom to move it forward, during which pressure is applied radially to its corners at its front end to reduce those corners and sink the bloom progressively from end to end. As fast as sinking occurs, the reduced inside of the advancing bloom is expanded to a circle having a diameter greater than the diameter of the passage before sinking. Simultaneously with said internal expanding the advancing bloom is compressed radially inward into circular cross section to form a cylindrical tubular body having an inside diameter greater than the diameter of the passage before sinking.

United States Patent 441,375 11/1890 Nortonetal lnventor Appl. No.

Filed Patented Assignee Priority Albert 11. Calmes Lausanne, Switzerland Nov. 5, 1968 Mar. 16, 1971 Jean-Paul Calmes LeMont-sur-Lausanne, Switzerland Nov. 8, 1967 Luxembourg PROCESS FOR MANUFACTURING CYLINDRICAL References Cited UNITED STATES PATENTS Primary Examiner-J. Spencer Overholser Assistant ExaminerR. Spencer Annear Attorney-Brown, Critchlow, Flick & Peckham ABSTRACT: Metal is cast to form a bloom that is polygonal in cross section with an axial passage extending through it. Pressure is applied to one end of the hot bloom to move it forward, during which pressure is applied radially to its corners at its front end to reduce those corners and sink the bloom progressively from end to end. As fast as sinking occurs, the reduced inside of the advancing bloom is expanded to a circle having a diameter greater than the diameter of the passage before sinking. Simultaneously with said internal expanding the advancing bloom is compressed radially inward into circular cross section to form a cylindrical tubular body having an inside diameter greater than the diameter of the passage before sinking.

Patented March 16, 1971 3 Sheets-Sheet 1 INVENTOR. ALBERTMCALM-S fiwamdwawm ATTORNEYS.

IPRGQESS FOR MANUFACTG CYLINDCAL TUBULAR METAL BQDES The pipeand tube-manufacturing industry has recognized for a long time the economic advantage of obtaining a high yield from liquid steel and the qualitative advantage of having steel of a uniform chemical composition for the manufacture of seamless pipes from continuously cast steel blooms, and it has tried to profit from these advantages industrially. Up to now, small square continuously cast blooms 4 inches to 6% inches wide have been used for the manufacture of seamless pipes on push-bench mills, after piercing in conventional hydraulic piercing presses. Trials are still being made to charge round continuously cast blooms of 6% inches CD. into a pilger mill plant after they have. been pierced in a crossroll piercer. 7

These eflorts have not led to any noticeable progress in the use of continuously cast blooms in the seamless pipe industry, because the same physical laws that apply to the pouring of ingots are valid for the continuous casting of steel; viz. with the heavier bloom sections and drastic external cooling of the hot bloom, the formation of a porous, spongy, and sometimes hollow central core of the cold bloom cannot be avoided. After air or furnace oxidation, this central zone cannot be welded together in the subsequent rolling deformation.

Round cast shapes of greater diameter than 6% inches, with drastic cooling of the hot bloom, are subject to the formation of longitudinal shrinkage cracks or fissures, which can in any case only be avoided or limited by applying rather low casting speeds. The continuous casting technique for round hollow blooms has the aim of obviating this latter inconvenience, and of forming a clean, sound surface of the hollow bloom bore, but nonetheless the tendency to create external longitudinal cracks still persists when casting round hollows.

Another important disadvantage of the continuous casting method for round hollow blooms derives from the necessity of introducing hot steel jet into a wide annular gap between the mold wall and the inside cooling case in order to avoid splashing and turbulence, which lead to poor surface quality of the hollow bloom. Therefore, with this technique, it is only possible to produce a thick-walled round hollow bloom, for instance inches wall thickness for 14 inches OD. The central passage is relatively small and must b--e expanded, which can only be done by a crossroll expander, but the ratio of wall thickness to outside diameter W/D is, with a value of 0.35, far too high for subsequent economic conversion into round hollow bars by reduction of outside diameter and wall thickness through crossrolling or longitudinal elongation.

Moreover, a continuously cast round hollow bloom has a porous and spongy ring zone at about two-thirds of the way from the outer to the inner surface of the wall. Before submitting such a hollow bloom to a crossroll reducing and elongating operation, during which high tensile and shearing stresses on the steel exist, this porous and spongy ring zone has to be compressed and welded up by radial and axial pressure forces.

In accordance with this invention, a polygonal hollow bloom, which most advantageously can be cut from a continuous casting of the same shape, is converted in the pouring heat, after temperature equalization in a holding furnace, into an elongated cylindrical tubular body that can be further processed into seamless pipes. The conversion of the polygonal hollow bloom into the cylindrical hollow body is accomplished in a two-high mill that I call a press-rolling mill. The rolls in the mill are provided with circular grooves that form a circular roll pass. The hot hollow bloom is pushed axially into the mill and is advanced by axial and radial forces over a stationary plug of circular cross section to form a round hollow body having a smaller perimeter than that of the polygonal bloom but with an inside perimeter greater than that of the passage through the bloom before rolling. As the bloom travels through the press-rolling mill the mushy, spongy zone in its wall is closed. It is necessary to start with a hollow bloom polygonal in shape because only such a bloom can be processed into a cylindrical tubular body without harm to the steel.

The bloom is pushed into the mill rolls and onto the expanding plug by a force compatible with the resistance of the hot steel section. The rolls exert a radial pressure on the bloom corners and thereby reduce them. The rolls also sink the bloom before it engages the plug. As the sides of the bloom are flat, it can be elongated substantially in circular rolling grooves without undue spreading of the steel in the gaps between the rolls. The initially relatively small axial passage through the bloom, made even smaller by the sinking, is expanded over the plug, and the porous spongy zones in the wall of the bloom are made compact and eliminated by the applied axial and radial pressures of the pusher and'the mill rolls. There is no harm to the steel structure of the blank.

Although continuously cast hollow blooms of different polygonal shapes may be used, a hexagonal shape is preferred because it provides around 12 to 15 percent more cooling surface than that of a round hollow shape of equal cross section. Moreover, the hexagonal shape has the advantage that the round grooves of the forming rolls of the press-rolling mill grip the bloom at six points, instead of at four points when a square hollow bloom is used, so the deforming-process exerts a more uniform stress on the steel. The hexagonal shape is also more favorable than the octagonal shape, because the latter approaches the unfavorable round shape too closely. By also making the shape of the bore or passage through the bloom hexagonal, with its sides parallel to the outer sides of the bloom, more uniform cooling of the bloom wall is effected.

A second feature of the invention is that, during the sinking phase in the press-rolling mill before the inside wall of the bore comes in contact with the expanding plug, the previously formed inside scale is disrupted or loosened and is removed backwards through the bore by high-pressure fluid jets issuing from a nozzle forming the head of the plug.

In the event that there is adhesive, sticking scale present on the inside wall of the hollow bloom, oxygen and ethylene can be conveyed through the plug holder bar and the plug to the nozzle head of the plug, and burned in the hollow bloom bore to liquefy the scale and hot scarf the inside wall. In order to convey the slag thus produced out of the bore easily, the pressrolling mill may be inclined backwards.

Another feature of the invention consists in the fact that the round hollow body that is produced by the process disclosed herein is obtained in a perfect circular shape and is perfectly straight, which permits it to be hot scarfed on the outside without useless scarfing losses.

A further feature of the invention consists in the subsequent immediate rolling and elongating, in the same pouring heat, of the scarfed hollow bloom in a multistand round hollow bar mill on a speed-controlled, stepped mandrel bar, pressure lubricated from the inside, into round hollow bars as a semiproduct for the manufacture of seamless pipes.

Apparatus for practicing this invention is illustrated in the accompanying drawings, in ,which:

FIG. 1 is a schematic vertical section of the apparatus;

FIG. 2 is a fragmentary plan view of the apparatus;

FIG. 3 is an enlarged fragmentary vertical section taken on the line Ill-III OF FIG. 2;

FIG. 4 is a horizontal section taken on the line IV-IV of FIG. 1;

FIGS. 5, 6, 7 and 8 are vertical sections taken on the lines V-V, VI-Vl, VII-VII and VIII-VIII, respectively of FIG. 3; and

FIGS. 9, 10, 11 and 12 are cross sections of other polygonal blooms that can be used in this process.

Referring to FIG. 1 of the drawings, liquid steel from a ladle l is poured through a tundish 2 into one or more continuous casting molds 3, by which the steel is continuously molded into a hollow casting 4 of any desired length. The casting is polygonal in cross section, preferably hexagonal as shown in FIG. 4, and the axial passage 5 through it most suitably is the same shape so that the wall thickness of the casting is uniform.

The casting descending from the mold is guided in a curve to a horizontal position by means of rows of rollers 7, between which water from sprayers 8 is sprayed onto the casting to cool it to some extent. From this cooling apparatus the casting enters a multistand two-high mill 9, in which it is straightened and sized. As the casting leaves the mill, suitable known apparatus in the form of an oxygen cutting machine 10 severs the casting into blooms 11 of the desired length. Each separate bloom is then moved laterally into one end of a temperatureholding furnace 12, in which the temperature of the bloom is equalized as the bloom travels through the furnace. When the bloom leaves the far end of the furnace it passes through outside descaling apparatus 13, utilizing high-pressure water, after which it is advanced through a corner sizing mill l4 and then moved laterally to the receiving table 15 of my pressrolling mill l6.

As shown in FIGS. 3 and 6, this mill is formed from two vertically spaced rolls 18, each provided with a circumferential groove 19 so that at the center of the roll pass the grooves form a circular opening. In the roll pass there' is an ogival plug 20 that is circular in cross section. The largest diameter of the plug is at the center of the pass. The plug is supported on the front end of a tubular bar 21, the rear end of which is rigidly supported in a well-known manner.

At the front or entrance side of the mill and extending into the roll grooves there is a rigidly mounted guide 23, the interior shape of which is such that the bloom on the receiving table will fit in the guide, with two opposite sides of the bloom vertical as shown in FIG. 5. At the exit side of the mill there also is a stationary guide 24, but the passage through this one is smaller and is circular to fit around the cylindrical hollow body issuing from the mill, as shown in FIG. 8.

When the bloom on the receiving table 15 has been lined up with entrance guide 23 of the press-rolling mill, a hydraulically actuated plunger 26 is moved forward into engagement with the rear end of the bloom, which it then pushes forward into the entrance guide. The six front corners of the bloom engage the mill rolls first (FIG. 6) and then, as the bloom advances, its front end is sunk to reduce both its inside and outside diameters at the same time, as shown in FIG. 3. As the front end of the bloom is sunk its inner surface comes into engagement with the nose of plug 20 and then slides over the plug. Since the major diameter of the plug not only is greater than the diameter of the sunk front end of the bloom passage, but also of the rest of the passage behind it, the advancing bloom is expanded internally by the plug. At the same time, the mill rolls are compressing the bloom around the plug until the bloom becomes circular at the center of the roll pass, as shown in FIG. 7, so the cross-sectionalsize and the wall thickness of the bloom are reduced and it becomes round inside and out. Since these actions of the rolls and plug on the bloom continue as the bloom is pushed over the plug, the corner reduction, sinking bore expanding and rounding of the bloom progress from one end of the bloom to the other, whereby a cylindrical tubular body 27 issues from the roll pass and moves through the exit guide 24.

Sinking of the bloom generally will loosen inside scale, which can be removed continuously by blowing it out of the rear end of the bloom and into and down out of a passage 28 in plunger 26. For this purpose the front end of plug 20 is provided with a multihole nose or noule 29, to which fluid under pressure, such as water or air, can be delivered through a central pipe 30 in plug bar 21. If the scale sticks to the side of the bloom passage and will not loosen, it can be liquefied and turned into slag by delivering oxygen and ethylene to the nozzle through concentric pipes 31 and 32 in the plug bar. The mixture is burned as it leaves the nozzle to hot scarf the inside the bloom.

After the bloom has passed completely through the pressrolling mill and plug 20 has been withdrawn through the resulting tubular body 27, the latter is moved sideways to a position in front of a scarfing ring 34, through which it then is pushed for scarfing the outside of the hollow body if the quality of the finished pipe to be made from that body requires complete removal of all imperfections. The tubular body, still in the pouring heat, then is fed into multistand hollow bar mill, such as shown in my U.S. Pat. No. 3,394,568, where it is rolled on a stepped, hollow, speed-controlled mandrel bar, pressure lubricated from the inside, into a round hollow bar that may have various final diameters, depending on the sizes of finished pipes required.

By practicing the present invention, it is possible to start with a big continuously cast polygonal hollow bloom, which is easy to pour,and to convert it into a round hollow body in the disclosed press-rolling mill, which is the only rolling mill capable of starting from polygonal hollow shapes and producing sound, cheap, round hollow bodies of a smaller diameter in long lengths with a, much bigger axial bore than that of the initial polygonal hollow bloom. For example, from one single hexagonal hollow bloom having a square inch cross section, equal to the cross section of a 13 inch square plain solid bloom (which however cannot be used for the manufacture of seamless pipes because of the oxidized spongy or hollow central core) it is possible to produce all round hollow bars for the manufacture of seamless pipes in the range of l inch 0.0. to 13% inch 0D. in the multistand pipe mill shown in my U.S. Pat. No. 3,394,568. The process disclosed herein permits the pouring of polygonal hollow blooms of great cross section with high productive capacity in the pouring heat, the improvement of the quality of the steel structure during the conversion to round hollow bars, and the production of these hollow bars, in a wide range of sizes from one single standard hexagonal hollow bloom. The process therefore makes available a cheap and sound semiproduct for the manufacture of seamless pipes. A most important advantage of this process derives from the fact that the charged weights of hollow bars can be much greater than hitherto, because they are not limited by the unit length of the raw material.

Flat sided blooms (square, rectangular or octagonal, as shown in FIGS. 9 to 12, or hexagonal) do not crack as easily as round blooms. The surface of a bloom per unit volume is greater for flat-sided than for round hollow blooms and therefore the cooling effect and subsequently the cooling speed or the production capacity is greater.

Iclaim:

l. A process for manufacturing cylindrical tubular metal bodies with uniform wall thickness, comprising casting a bloom that is polygonal in cross section with an axial passage extending entirely through it; applying pressure to one end of the hot hollow bloom axially thereof to move it forward; applying radial pressure to the corners of the polygonal bloom at its front end to reduce those corners and sink the bloom progressively from end to end as the bloom advances; applying an internal expansion force to the advancing bloom in the area in which sinking is occuring to progressively expand the reduced passage of the bloom from end to end to a circle having a diameter greater than the diameter of said axial passage before sinking; and, simultaneously with said internal expanding, compressing the advancing bloom radially inward into circular cross section to form a cylindrical tubular body having an inside diameter greater than the diameter of said passage before sinking.

2. A process according to claim 1, in which the polygonal bloom is cast with said axial passage therethrough the same shape as the outside of the bloom.

3. A process according to claim 1, including the step of delivering oxygen and ethylene to said bloom passage and burning them to liquefy sticking inside scale.

4. A process according to claim 1, including the steps of cutting said bloom from the front end of a continuously cast hollow polygonal casting of indeterminate length as the casting is being formed, bringing the bloom to a uniform rolling temperature, descaling the outside of the bloom with highpressure water, sizing the bloom, scarfing the inside of the bloom during sinking, and hot scarfing the outside of the bloom.

5. A process of manufacturing cylindrical tubular metal bodies from blooms pushed lengthwise over a round plug centered in a circular roll pass formed by driven grooved rolls, the process comprising casting metal to produce a bloom that is polygonal in cross section and has an axial passage of smaller diameter than the plug extending entirely through it, pushing the hot hollow polygonal bloom lengthwise into contact with the rolls ahead of the circular pass so that the corners of the bloom at its front end will be compressed and the front end portion of the bloom will be sunk as the bloom approaches the 

1. A process for manufacturing cylindrical tubular metal bodies with uniform wall thickness, comprising casting a bloom that is polygonal in cross section with an axial passage extending entirely through it; applying pressure to one end of the hot hollow bloom axially thereof to move it forward; applying radial pressure to the corners of the polygonal bloom at its front end to reduce those corners and sink the bloom progressively from end to end as the bloom advances; applying an internal expansion force to the advancing bloom in the area in which sinking is occuring to progressively expand the reduced passage of the bloom from end to end to a circle having a diameter greater than the diameter of said axial passage before sinking; and, simultaneously with said internal expanding, compressing the advancing bloom radially inward into circular cross section to form a cylindrical tubular body having an inside diameter greater than the diameter of said passage before sinking.
 2. A process according to claim 1, in which the polygonal bloom is cast with said axial passage therethrough the same shape as the outside of the bloom.
 3. A process according to claim 1, including the step of delivering oxygen and ethylene to said bloom passage and burning them to liquefy sticking inside scale.
 4. A process according to claim 1, including the steps of cutting said bloom from the front end of a continuously cast hollow polygonal casting of indeterminate length as the casting is being formed, bringing the bloom to a uniform rolling temperature, descaling the outside of the bloom with high-pressure water, sizing the bloom, scarfing the inside of the bloom during sinking, and hot scarfing the outside of the bloom.
 5. A process of manufacturing cylindrical tubular metal bodies from blooms pushed lengthwise over a round plug centered in a circular roll pass formed by driven grooved rolls, the process comprising casting metal to produce a bloom that is polygonal in cross section and has an axial passage of smaller diameter than the plug extending entirely through it, pushing the hot hollow polygonal bloom lengthwise into contact with the rolls ahead of the circular pass so that the corners of the bloom at its front end will be compressed and the front end portion of the bloom will be sunk as the bloom approaches the circular pass, continuing said pushing to force the bloom over the plug to thereby expand the inside of the advancing sunk portion of the bloom to a circle having a diameter as great as the plug while the rolls simultaneously compress the bloom into circular cross section around the plug, and continuing advancing of the bloom completely through the circular roll pass to form the bloom into a cylindrical tubular body having an inside diameter greater than the diameter of said passage before sinking. 